Button cells conventionally comprise a housing consisting of two housing halves: a cell cup and a cell top. These may, for example, be produced as stamped parts from nickel-plated deep-drawn sheet metal. Usually, the cell cup is positively poled and the housing top negatively poled. The housing may contain a very wide variety of electrochemical systems, for example, zinc/MnO2, primary and secondary lithium systems, or secondary systems such as nickel/cadmium or nickel/metal hydride.
The liquid-tight closure of button cells is conventionally carried out by crimping the edge of the cell cup over the edge of the cell top, in combination with a plastic ring which is arranged between the cell cup and the cell top and is used simultaneously as a sealing element and for electrical insulation of the cell cup and the cell top. Such button cells are described, for example, in DE 31 13 309.
As an alternative, however, it is also possible to manufacture button cells in which the cell cup and the cell top are held together in the axial direction exclusively by a force-fit connection, and which correspondingly do not have a crimped cup edge. Such button cells and a method for their production are described in unpublished German patent application 10 2009 017 514.8. Regardless of the various advantages which such button cells without crimping may present, they nevertheless cannot withstand such high stresses in the axial direction as comparable button cells with a crimped cup edge, especially as regards axial mechanical loads which originate from inside the button cell. For example, the electrodes of rechargeable lithium ion systems are constantly subjected to volume changes during charging and discharging processes. In button cells without crimping, the axial forces occurring in this case can naturally cause leaks more easily compared with button cells with crimping.
A solution to this problem may be found in unpublished German patent applications 10 2009 030 359.6 and 10 2009 008 859.8. Inter alia, references may be found therein to button cells comprising a housing having a plane bottom region and a plane top region parallel thereto, an assembly consisting of flat electrode layers and separator layers in the form of a preferably spiral-shaped electrode winding being arranged in the housing in such a way that the end sides of the winding face in the direction of the plane bottom region and the plane top region. The electrode layers of the winding are thus oriented essentially orthogonally to the plane bottom and top regions of the housing. As a result of this, radial forces such as occur during the aforementioned charging and discharging processes of lithium ion systems can in principle be absorbed better than in the case of conventional lithium ion button cells, in which electrode layers are arranged stacked in parallel alignment with the plane bottom and top regions.
Windings consisting of flat electrode layers and separator layers can be produced quite straightforwardly using known methods (see, for example, DE 36 38 793) by the electrodes being applied, in particular laminated, particularly in the form of strips, flat onto a separator provided as an endless band. The assembly consisting of the electrodes and separators is generally wound on a so-called “winding mandrel.” After the winding has been removed from the winding mandrel, an axial cavity is left at the center of the winding, the effect of which is that the winding may possibly expand into this cavity. This, however, can sometimes lead to problems in the electrical contact of the electrodes with the metal housing halves.
It could therefore be helpful to provide a button cell in which the aforementioned problems do not occur, or only occur to a greatly reduced extent.